1. Field of the Invention
The present invention relates to a magneto-optical recording medium capable of recording, reproducing, and erasing etc. information by a laser beam, and the like. Particularly, the present invention relates to a highly reliable magneto-optical recording medium, comprising a metal recording layer having an easy axis of magnetization perpendicular to the layer surface thereof, in which recording and reproducing of information is obtained by the magneto-optical effect.
2. Description of the Related Art
Optical recording media have been widely investigated and developed since they are capable of high density and large capacity recording of information. Particularly, magneto-optical recording media can be utilized in various fields and therefore, various materials and systems therefor have been proposed and will be practically utilized.
As such materials proposed for the magneto-optical recording media are FeTb (Japanese Unexamined Patent Publication No. 52-31703), FeTbGd (Japanese Unexamined Patent Publication No. 56-126907), FeTbCo and FeCoDy (Japanese Unexamined Patent Publication No. 58-73746), FeNd (Japanese Unexamined Patent Publication No. 61-165846), etc. Nevertheless, further improvements of the recording and reproducing characteristics and durability, including a resistance to oxidation of the recording materials, are necessary before the erasable magneto-optical recording media becomes practically utilizable, since the materials for the magneto-optical recording are very susceptible to a corrosion such as oxidation.
Attempts have been made to realize the above objects by covering both sides of the recording film, and adding various elements to the recording film. Currently, transparent dielectrics of AlN, Si.sub.3 N.sub.4, ZnS, SiO, Y.sub.2 O.sub.3, etc., among others, are considered preferable for the protecting layer, but the permeation of oxygen and water from the atmosphere as well as permeation and diffusion of water and chlorine from the transparent plastic resin substrate cannot be completely prevented, and thus the recording film is deteriorated. With regard to the addition of elements, although some effectively prevent corrosion of the recording film, they disadvantageously cause a reduction of the Kerr rotation angle. In this respect, preferably the protecting layer prolongs the life of the recording film without lowering the characteristics thereof. Therefore, the development of a protecting film or films which effectively prevent a permeation and diffusion of oxygen, water and chlorine, etc. is important.
To this end, a metal protecting layer of metal titanium alone or a combination thereof with dielectric layers as mentioned above has been proposed as an effective protecting layer (EP-A-0245833). Nevertheless, upon investigation of this protecting layer by the inventors, it was found that further improvement is necessary because pin holes were formed during high temperature and high humidity environment resistance tests and the recording film was deteriorated by chlorine or an acid remaining in the resin of an organic protecting layer when applied.